Hi Jeremy,
if you can get the back off your watch there is a little lever that you can move to speed up or slow down your watch.
I have no practical experience of this !
So I can't say how much you could expect to adjust this way ( seconds or minutes per day ).
Also I should imagine it is quite "Hit & Miss" adjusting a watch without the correct measuring equipment. My watchmaker has a vibrograph ( I think that's what it is called )
He puts the watch on it & it measures the beats, he can measure the watch in a number of positions.
Within a very short time ( less than a couple of minutes ) he can adjust a watch.
Whether the watch runs accurately on a wrist is another thing though...... sometimes my wrist is hanging down ( slow walking ), sometimes its "flat" ( sitting at a PC), sometimes it's wildly moving around ( Jogging, doing some house work ) etc etc. The watch be run & behave differently depending on your wrist position/movements.
The fine art of setting watches accurately is to find the best compromise for the wearer.
eg if you spend all day working as a ski instructor, your wrist moveemnts are different from those of a bar tender or computer programmer etc etc.
Good luck with your adjustments, let us know how you get on.
Steve