1. Make a clean source backup first
Close the current session and copy the Valheim save location before moving anything. Valheim 1.0 changed the save format, and recent hotfixes have already addressed save-conversion issues, so keep one untouched source copy until the new server is verified.
2. Identify the active save location
The official dedicated-server guide documents the default Valheim save folder on Windows and Linux and also supports a custom -savedir. Copy the active world from the location your current game/server is actually using, not from an old backup folder.
3. Keep the world name consistent
Iron Gate's server argument -world "Dedicated" creates a world with that name or loads an existing world of the same name. Configure the new server to load the migrated world rather than accidentally creating a fresh empty one.
4. Choose Steam or crossplay backend deliberately
If the group includes Xbox, PlayStation or Switch 2 players, the new dedicated server needs the crossplay backend. Iron Gate documents -crossplay for PlayFab and notes that crossplay servers can be joined by Join Code/public route rather than local or loopback IP.
5. Test before deleting the old copy
Launch the migrated server, verify a known base and inventory location, confirm that the correct world loaded, then test the actual platforms your group uses. Do not delete the original copy just because the server starts once.
6. If moving to a managed host
Use the host's documented save-upload/import workflow and retain your own offline backup. A managed host can remove the always-on-PC and update burden, but it does not replace your responsibility to keep a recoverable copy of a long-running world.
Official references
Iron Gate dedicated-server guide · Valheim 1.0 FAQ · Patch 1.0.15 save recovery note
Unofficial guide. Product and game names belong to their respective owners. Always check current official patch notes before changing a server or important save.