If you are happy that it is the lifter then as the others said, drive it around and it should clear. How long this takes is unknown...a piece of string comes to mind but should clear within 20 mins or so. Mine had this about a month ago after not being used...cleared after 10 mins...I decided to flush the system and renewed oil/filter anyway. I ask ' if you are happy it's a lifter' as to tell a little story many years ago I had what I thought was a stuck lifter, even if a little loud, it did eventually clear. Much later I found the real cause which was a chunk of ceramic isolator casing which had broken off no. 2's iridium spark plug which then got broken up between head and piston until the remains where presumably expelled through the exhaust. This had no effect on performance as the car still gave the highest BHP of any car at the dyno run later that very day. Only one power run was performed due to a hesitation felt at WOT which of course was due to the damaged plug, not known at the time. Back then some dyno's refused to run with iridium plugs for this very reason, things have changed now as branded iridium plugs are easily available, back when these plugs were new there was a lot of bad ones about.
Anyway, just a story to say that its not always the lifter but still most likely to be.
Good luck
Pete