The leaves are curling and seem to have holes in the leaves
Lilac Tree Only One Blossom and Leaves Curling
Lilacs are generally tough and rarely troubled by disease or pests. Much more frequently, they don't flower as owners hope. This article will suggest a few reasons, and steps you can take to increase the health of your tree: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-bush-not-blooming.htm
Spraying with neem oil will help get rid of
any bugs that might be causing holes and crinkled leaves:https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm
Use oil at a rate of 2 tablespoons per gallon of water.