In the "unit_variants_tables" under "unit" you can not, as shown in Sebidee's Complete Guide, type or paste your new units key; instead there is a scroll-down from which you, surprisingly enough, cannot choose your unit's key.

The same is relevant for both "units_custom_battle_permissions_tables" and "units_to_groupings_military_permissions_tables" under "unit".
What to do? What to choose from the scroll-down under "unit" in these cases where you cannot type your unit key/name?

I use PFM 5.2.4 (TWH2)

Thanx