Fertilizing is not rocket science, though many folks seem to want to make it that way.
Go to your local nursery, big box store, garden center, etc., and buy almost any houseplant fertilizer. Every box/package/bottle of fertilizer sold in the USA is supposed to have an analysis of its contents on the label. Look for one with fairly even numbers after Nitrogen Phosphorous and Potassium, like 8-10-15, or 10-15-30, etc. (Don't buy one that has a zero after one of those).
Follow directions on the label to mix (if necessary). Fertilize every 2 weeks at concentration directed on the label.