This is a normal EDB entry for a church, what i've marked in red will convert catholic religion 5% per turn. From your post i assume you have no capability entry!
Code:
building temple_catholic
{
convert_to temple_catholic_castle
religion catholic
levels small_church church abbey cathedral huge_cathedral
{
small_church city requires factions { denmark, hre, scotland, france, england, hungary, poland, venice, papal_states, portugal, spain, sicily, milan, }
{
convert_to 0
capability
{
agent priest 0 requires factions { denmark, scotland, hre, france, england, }
agent priest 0 requires factions { hungary, poland, }
agent priest 0 requires factions { papal_states, portugal, spain, sicily, milan, venice, }
happiness_bonus bonus 1
religion_level bonus 1
pope_disapproval 1
agent_limit priest 1
}