I hung it on a door so that I could gradually work out what to do with it. It was a bit of a puzzle.
Below are the stages I went through to do it. Obviously, the shirt might not be to your taste but the principles apply to remaking any large boxy shirt into something wearable.
Cut to length & hem
Remove old & add new buttons. Make extra buttonholes. The shirt just had too few buttons to hold together properly.
Make tabs to shape the front. Tabs are at the waist for both back & front.
Decide on sleeve length. Cut, finish raw edge and bind sleeve.
And that’s it!