I went to my uncle's house today to have him fix my grandmother's glasses.
この場合、次のような言い方ができますよ。
ーI went to my uncle's house today to have him fix my grandmother's glasses.
「今日は叔父の家に行って、祖母のメガネを直してもらった」
to have someone fix XX で「人にXXを直してもらう」と言えます。
ご参考まで!