Hello I received this message from Google but I do not know how to fix these issues
Warnings are suggestions for improvement. Some warnings can enhance your appearance on Search; some might become errors in the future. The following warnings were found on your site:
No global identifier provided (e.g. gtin, mpn, isbn)
Missing field ‘review’
Missing field ‘aggregateRating’
Missing field ‘priceValidUntil’ (in ‘offers’)
Invalid object type for field ‘brand’
We recommend that you fix these issues when possible to enable the best experience and coverage in Google Search.
If anyone understands this please let me know. Thank you.