How to let user submit an item on database but limited to only 1 row per user

[J.D]

You can set the _id field to be the _id of the collection record.
If you use a dataset, use setFieldValue(‘_id’, userId ) . See here .

put all the fields in infoObject, the:

infoObject._id = userId;
wixData.save('CollectionName', infoObject),