To Damage
する verb
If 損害 is "damage" then the verb version would be to damage.
そんがいする
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own. Reading is the same as 損害 as well.
彼の言葉を信じて投資信託を買ったんですが、結局大きく損害してしまいました。
I believed what he said and bought an investment fund, but I ended up losing a lot of money.