How or should I prune my lilac bush as it didn’t get it this spring?

You should only prune a lilac bush right after is has bloomed and the flowers are dead. The buds for the next year sprout in june so if you trim it now it may not bloom next year

Trim off all the spent flowers/seeds. Then decide how much of the bush you wish to prune.

Hello R_s.

Knowing when to trim lilac bushes is important. Most lilacs don’t require pruning until they reach about six to eight feet tall. The best time for pruning lilac bushes is right after their flowering has ceased

Read more at Gardening Know How: Pruning Lilac Bushes: When To Trim Lilac Bushes

https://www.gardeningknowhow.com/ornamental/shrubs/lilac/pruning-lilac-bushes-when-to-trim-lilac-bushes.htm

https://extension.unl.edu/statewide/douglas-sarpy/pdfs/ce/resources/ce-g1860-lilacs.pdf

https://www.marthastewart.com/270986/lilacse