To do "lateral" balance (port and starboard or side to side) can be done several ways but to do it by yourself:

Keeping the plane right side up, set the very tip of the bottom of the tail (not the elevator but either the rudder, if you can or the tip of the fuselage at the tail) on the edge of a table, paint can or whatever, then making sure that the engine is not on the compression stroke, hold the front of the plane by the spinner, prop bolt (NOT THE PROP ITSELF) while holding onto a wing making sure to keep wing and the plane level, now let the wing go and see which wing drops, the wing that drops is the heavy wing. Do this several times and if each time the plane drops to a certain side, then you need to add weight to the opposite wing which is the light wing. If the plane randomly drops a wing, meaning it drops one way then the other and equal amount of times, then the balance is close enough, if it drops more times to one side then the other then again that is the heavy wing.

Having 2 people makes this job easier since one can hold the front and the other can hold the back.

Get some stick on lead weight from the LHS, set them on the top of the light wing at the tip until you get the balance right, then tape the weight to the bottom of the wing at the tip with good strong nylon or fiberglass reinforced tape. You can also cut into the covering and glue the lead inside if you do not want to see the weight on the outside which is my perferred way but you need to reseal the covering with a piece of tape or iron on a patch of covering.