Conversion from bromine to chlorine pretty much involves draining and refilling.

The solid form of bromine contains bromine and a hydantoin carrier. This carrier chemical accumulates and apparently inhibits the conversion of bromide (left over bromine that can be regenerated to bromine by chlorine) into bromate, which does not regenerate.

The regeneration process means that, as long as 2 - 5 ppm of bromide remains in the pool, you can not have a chlorine pool, because added chlorine simply regenerates the bromide to bromine and is destroyed in the process.

The presence of hydantoin means that the small fraction of bromide that would have been converted to bromate, instead of bromine, instead also regenerates to bromine.

Conversion of all the bromide to bromate is the only method -- other than draining and refilling -- of 'converting' from a bromine pool to a chlorine pool -- but the presence of hydantoin inhibits that.

However, do NOT drain your pool!

You must FIRST confirm that you CAN drain it safely. If you have a liner, you can not. If you have a fiberglass pool and are not on a hill side, it's iffy. If you have a concrete pool in a flat damp area . . . it's STILL risky.