持ってていいよ

you can keep it

→ 持つ
phrase Rare #29,214
you can keep it A casual way to give permission to keep or hold onto something. 持ってて is a conversational contraction of 持っていて.
JA: この本、もう読んだから持ってていいよ。
EN: I've already read this book, so you can keep it.

持ってていいよ

You can keep it.

— ジョジョ・ラビット (2019)

明日までこのテープ持ってていいよ

You can keep this tape until tomorrow.

必要ならこの辞書は持ってていいよ

If you need it, you can keep this dictionary.

これ自分用に持ってていいよ

You can keep this for your own use.