De or het conversieregeling?

The correct Dutch article is:

de conversieregeling

Rule Words ending in -ing: almost always de. See the rule

How to use conversieregeling

the conversieregelingde conversieregeling
this conversieregelingdeze conversieregeling
that conversieregelingdie conversieregeling
our conversieregelingonze conversieregeling
your conversieregelingjouw conversieregeling
every conversieregelingelke conversieregeling
which conversieregeling?welke conversieregeling?
a big conversieregeling / the big conversieregelingeen grote conversieregeling, de grote conversieregeling