Migrating to Linker

Linker needs no import. It builds on the native Jira links that already exist on your work items, whatever created them: another linking app, a Jira Data Center instance, or people linking by hand. Migration is therefore short: install Linker, create and configure a field, run a resync, and the fields fill themselves from the links that are already there. Nothing has to be re-linked.

The links are the data. A linking app that creates real Jira links stores the truth in the same place Linker does: Jira's own links, visible under Linked work items. That is why switching needs no export and no import. The new field simply adopts the links it finds.

From Linksy or another linking app

If you come from Linksy or a similar app, the concepts map almost one to one:

In your current app	In Linker
The custom field and its scheme or context settings	A Linker field with one configuration per context: see the Configuration reference
The work item panel	A Linker panel, defined on the Global panels page
The resync or bulk sync	A resync, started from the Fields page
Dynamic JQL placeholders	`currentIssue()` in any Linker JQL: see the JQL guide

The switch itself:

Keep the old app for now. Leave it installed and untouched until you have verified the result. Running both apps side by side during the switch is fine.
Create the Linker field. Use the Create custom field button on Linker's Fields page (Jira Settings (gear) → Apps → Linker → Fields) or Jira's field wizard: see Getting started.
Add it to the same screens as the old app's field, so people find it in the familiar place.
Configure each context. Set the link type and direction to what the old app used, and check the picker filter and delete behavior. If the old field had different settings per space, create matching contexts: see the Configuration reference.
Preview with a dry run. Open the resync dialog from the Fields page and tick Preview only (dry run). It reports how many work items would change and writes nothing.
Run the real resync. The fields fill from the existing links. Repeat per context if the field has several.
Verify a few work items. Compare the Linker field with the Linked work items section and with the old app's field. Also try the picker and, if you use one, the panel.
Retire the old app. Remove its field from the screens, uninstall the app, and update saved filters, boards and dashboards that still reference the old field by name.

Old field values do not transfer, and they do not need to. The old app's values live in that app's own custom field, which no other app can read. But if the old app created real Jira links (Linksy and most others do), the links carry the truth, and the resync rebuilds the field values from them. Check this before you start: open a few work items and look at Linked work items. An app that only stored field values without creating links leaves nothing behind to adopt.

Adopted links stay protected. Linker treats links taken over by a resync like links made by hand: in the default delete mode, deselecting such a work item later never deletes the link. See Resync & migration.

From Jira Data Center to Cloud

Native work item links survive the move to cloud: Atlassian's Jira Cloud Migration Assistant migrates them together with the work items. Apps are a different story: Data Center apps and their custom fields do not migrate as apps, so a linking field from a Data Center app arrives in the cloud as nothing more than the links it created. Those links are exactly what Linker needs.

Finish the Atlassian migration first. Run the Jira Cloud Migration Assistant and confirm the work items and their links arrived: spot check Linked work items on a few migrated work items.
Install Linker in the cloud site from the Atlassian Marketplace.
Create and configure the field. Contexts, link type and direction, screens: the same setup as for any new field, described in Getting started and the Configuration reference.
Resync. Dry run first, then the real run, per context. The migrated links populate the fields.

The resync itself

Every path above ends in a resync. The dialog, the preview mode, the Keep existing field values option and the warnings about removed field values are all described on Resync & migration: read that page before the first real run.