Your brass is Boxer primed? Nice DI headstamp perhaps?
Decap it normally. Might take a bit more pressure.
You can buy primer pocket swagers from RCBS or Dillon. If you are processing a lot of brass, this might make sense.
You can ream out the crimp with: a sharp jack knife; your case neck chamfering tool; a sharp countersink. Don't cut away any more brass than necessary.
If the primers do not want to seat easily, there is still crimp present.
Before you proceed too far with your case prep, inspect the brass very carefully for signs of incipient separations. Lee
Enfield Rifles may be among the worst offenders when it comes to case separations. With assorted .303 range brass, I anticipate culling as much as 20%.