sounds like there is a break in the cable that leads to the right ear. try narrowing down where the break is by wiggling the cable all along the length of it. once you have found the break point you will want to replace that section of wire. If that doesnt find them problem it could be that the soldering on the jack or on the driver in the right ear has come loose( happens quite often)

try some needle nose pliers or a cotton bud cleaner with some glue on( insert the cleaner into the headphone jack so that it adheres to the old jack and once sealed slowly remove) try those before resorting to a full teardown.

sounds like there is a break in the cable that leads to the left ear. try narrowing down where the break is by wiggling the cable all along the length of it. once you have found the break point you will want to replace that section of wire. you will need some basic tools for this and some patience as it can be tricky. let me know if you need any more help.