Hi @zubbub ,
Does your deadbolt have two blocked "holes", in the cover plate, one either side of the key tumbler slot on the lock on the inside of the door?
If so, try inserting the key on the inside lock and slowly start turning the key to open the lock. At some point in the turn, the "holes" should no longer be blocked and either an appropriate sized Allen key (aka hex socket key) or a screwdriver(depends on maker) can be inserted and used to unscrew the inside lock away from the outside lock