Wondering how people apply heat to small screw heads.
Possibly heating the tip of a cheap, damaged old screwdriver in a flame then holding it in the slot or star of the screw head.
Or even drilling holes in a spare copper soldering iron bit as required, with a couple of assorted diameter rods driven into the copper bit.
A sort of multi tipped heater.
Soldering iron with tip has been mentioned.
If you have a steel, copper or brass tip, OR narrow copper nail, copper or brass or steel screw or nail, a strong, narrow jaw vice grip, some heat sink paste/jell, and a gas torch.
Take the probe tip, lock the tool in the back end of the probe with the vice grip/plyers apply a ring or three of heat sink material about two or three inched up from the tip, and with the camera/lens pre positioned, heat the top, just up to the heat sink until it's red hot and then apply it to the stuck screw of 30 - 60 up to 90 seconds anr remove the tip, reheat it to red and apply again.
Do several applications, then let the screw air cool.
It should have had enough expansion and then cooling to do the job.
I have some odd pieces of steel, 3/8" thick lettering dies, for striking into metal and wood, which includes a "dot" die, which would be ideal for this application and it's mass would hold a great deal of heat, needing a vice grip and heat sink to be used.
There are other methods and probs you can try, but in the past, I've had good results with other items, using this basic method, always metal on metal.