Martha...They have a kit that holds 1200 lbs. at Amazon that you might take a look and see if it will work for you...just 2 straps with hooks. Good luck!
Martha: maybe this will help
If it is a tire swing, throw a rope over branch and tie several knots. Tie to tire. If it is a board swing, we used a flat board with a semi circle cut off each end for the rope to slide in. Use a long rope that will tie to the branch, come down, go under the board, and back up the the branch to tie again the other end of the rope to the branch. The semi circles (like for regular rope) that are 1 inch or smaller across will hold the board in place while swinging. OR buy a swing with a chain and attach the chain to the rope on both sides. The board with slight knotches works just as well and for free except the rope.
I like the new nylon straps for hanging swings as they don't damage the tree... https://www.amazon.com/s?k=swing+hanging+straps&i=garden&ref=nb_sb_noss