Your ASA has what is known as a 15 degree outward angle to it. Also known as an "angled" asa. The only option is to purchase a straight one or have to do some magic and either reverse the one you have and route the wires for the noid through the hole which will be on the left side. Be sure that the reg doesn't interfere with the trigger guard and hopefully you have enough solenoid wire.
You may have issues with it clearing the trigger frame if you do that, plus the slit for the pump arm (or solenoid wire) will be on the wrong side.
Anyways, just flip the body upside down and look inside the Vertical ASA (adaptor the reg screws into ) and you will see bolt. You need a 1/4 inch 12 point socket to remove it. Flip around the ASA and screw the bolt back in. Then figure out if it the regulator will clear the trigger frame and what you are going to do about the solenoid wire.
There are aftermarket 15degree ASA's with slots on both sides that you may want to look at. Just make sure the regulator clears the trigger frame first.