The "cap thing" is the RH BB bearing cup. It is very tightly secured into the shell and is often called the "fixed" cup to indicate it's not changing it's position after install. These can be a struggle to remove if the right tools are not available.

First thing is to determine the cup's threading direction so you know which way to turn it to loosen/remove it. By using the LH cup one can measure that and assume that the RH cup is also of the LH's spec standard. By looking into the shell carefully one might see the RH shell's threads and thus their direction.

Next is the tooling. While I have used bench vices and huge adjustable wrenches held onto the cup/shell with a through bolt/washers using the correct BB Fixed Cup Wrench makes things much easier to set up. Since the amount of force that will likely be needed to loosen the fixed cup is very large any tool slippage will mean greater injury.

This, like some headset work, is better done by a shop if good results are wanted. Their stock of tools and prior experience can make what can be a knuckle busting and dent prone procedure (if done at home) into a safe and damage free one. Andy.