You should be able to move the lever itself. If there is no adjustment on the bike, then mark the spline & the gearchange lever with a pencil so you can rotate one way or the other. Remove the possibly 10mm nut at the bottom of the lever & the spline (where thesplit of the lever is snugged up on the gear change spline) also the above, probably 10mm bolt.
Then rotate the lever clockwise or counter clockwise, just a minor bit as the spline will be pretty fine, for the lever's new position, slide the lever back on the spline sort of check the lever's position, without shifting, & if okay then back with the bolt & nut.
Try the shifting & if not satisfactory then do the above again till fully satisfied. It is really quite an easy thing to do.