1. check the tyre at the opposite end is squished into the middle of the rim
2. pull the tyre up from the opposite tyre round to the end you cant get on (inch by inch)
3. put washing up liquid on the rim where its stuck
4. edge the tyre on mm by mm, don’t try to lever a large amount on.
FWIW, for 1. be sure to start opposite the valve and aim to have the last tight bit lined up with the valve. That’s the important bit. Then work round both sides equally one hand per side, pushing the tyre into the rim and edging the bead over. The last bit should go on easily then.