As far as I know, there isn't an account migration mechanism in Lemmy yet. I've heard (fourth hand at best) that it is in the works but hasn't been implemented yet. You may have to do it the hard way. Copy, paste and search.
Thanks for this, works like a charm and exactly what I needed. Especially nice that it does a delta and not simply overwrites the target profile (as I already had some new communities I was following in the target account).
Only thing I missed was a swap or reverse for Download and Upload, as I wanted to sync both accounts. Just meant I had to fill in both forms again, no biggie.