Remove the three screws that hold the assembly in. And then insert those screws into the other set of holes around the perimeter...tighten each a bit at a time (evenly) and they will essentially pull the assembly from the tank. Unseating the o-ring takes quite a bit of force, evenly distributed...which can only be done with the screws.
And order a new o-ring as you should refresh that rather than attempting to re-use the old o-ring. There's other threads about the process of reinstalling...you'll need to lubricate the o-ring with the proper lubricant and you'll need to buy three longer screws to aid in seating the assembly (once it starts to seat you can then remove the longer screws and put in the oem screws).
Edit: This is based on 916-era bikes. Just noticed you have an 1198...not sure if its the same.
Your fuel pump is the same on your 1198 as my 1098S and is actually the same as it was on my Sport Classic. Once you have the tank off and you've removed all the little screws on the pump base, I just grab the output/return fittings and a little tug and it comes lose. I've taken mine out twice since I got the 1098 and did my SC once. Never was it super tight where I wondered how the hell I could get it off. Truly, it required zero force, the screws held it down and with them removed it has always just fallen right out.
Well it took the mechanic at south sound over a hr to get the pump out. The zip tie failed and the pump had separated.
He had to disassemble the pump whilst it was still in the tank Then re assemble the pump,$184 later ouch.
At least I don't feel so inadequate for not being able to perform what should have been a simple task.