This will sound silly but you can easily check spoke tensions by plucking them like a harp - it will not tell you the right tension, but an unevenly tensioned wheel will have very differently sounding spokes, and it may then give you some ideas where to begin retensioning. If it is beyond anything minor and unless you know what you are doing, and have a jig, I would suggest taking it to a builder to retension
This will sound silly but you can easily check spoke tensions by plucking them like a harp - it will not tell you the right tension, but an unevenly tensioned wheel will have very differently sounding spokes, and it may then give you some ideas where to begin retensioning. If it is beyond anything minor and unless you know what you are doing, and have a jig, I would suggest taking it to a builder to retension