Since you actually have the Minna books, then I might suggest:
- Continuing on with the Genki II book (as @IcyIceBear suggest), since it will follow on from where you left off with Genki I, and there will be less ‘overlap’ between the two, by design.
- Use Bunpro’s Decks feature (requires opting-in to the Beta program; just go into your account Settings and opt in) to track your progress in Genki II using the Genki II Deck. Mark the Genki II Deck as your ‘Primary Deck’.
- Simultaneously mark the Minna no Nihongo 1 Deck as your ‘Secondary Deck’. This way, you can – at your own pace, whatever feels comfortable to you – also Learn items from the MNN books that maybe weren’t covered by Genki I and/or II.
- If an item you Learn from the MnN deck is easy for you to learn, just by using Bunpro alone, then great!
- If the item is a little too unfamiliar to you, well, “Hey, presto!” you actually have the MnN books available for you to reference. Just go to the chapter the item comes from and read about it directly from the book.
- With an actual textbook to ‘fall back on’, you can just follow Bunpro’s lead (which itself follows the same order of the lessons in the books), and thus easily cover any items that are in the MnN books, but not in the Genki books, without also having to re-study the stuff that’s already covered by the Genki books.
This way, you get to learn all the items from all the books you own. Since Bunpro treats grammar points as independent things – i.e. whether you’re learning する verb grammar from Genki or from Minna, it’s the same grammar point on Bunpro (する (JLPT N5) | Bunpro – Japanese Grammar Explained) – then by using Bunpro to help you select lessons from the Minna decks, there won’t be any overlap or missed grammar points. If you were only studying the books, without Bunpro, it would be harder to avoid such overlap.
Personally, I’ve used this primary/secondary decks feature to ‘fill in the blanks’ from all the beginner textbook decks, just so I know I have all the basic textbook grammar points covered. You don’t have to do this, but I kinda like it myself.
P.S. If you haven’t been using the Decks yet (i.e. if you’ve been using the standard Paths instead), then you may not have seen Bunpro’s Vocab study yet. Several decks – in particular Genki and Marugoto, but unfortunately not Minna no Nihongo – include not just the grammar points, but the vocab used in the books as well. Therefore, if you want to ‘pick up’ the vocab that was in Genki I, while you’re studying Genki II, you could temporarily make Genki I your secondary deck, and relatively quickly Learn vocabs from Genki I in the same way as described above. Once you’ve got the vocab from Genki I caught up, you can switch your secondary deck to MnN 1, and proceed as described.