Two suggestions.

1- Put enough air into the tube to give it shape before installing it. this makes it far easier to push into the tire and the shape keeps it well in the tire reducing the chance of pinching it between the tite and rim. You might have to bleed some of the air out as you finish the installation.

2- Mount the tire starting opposite and ending at the valve. Then gently push the valve in so as to bring the reinforced section at the base well up into the tire, ease the beads into position and pull the valve back down settling the tube above the tire.

One last thought, anticipating a future problem. If you're using a Presta valve tube with a rim drilled for Schrader valves, use a grommet or valve hole adapter to protect the base of the valve from the corners of the oversize hole. Otherwise there's a decent chance of the tube getting cut there, or the valve extruding out at high pressure. Years ago when there were no ready made adapters, I used the sticky fiber reinforcements they used to sell for looseleaf notebook pages. Just slide two of them glued to each other down the valve before installing the tube.