Hi,
you can search in multiple fields by combining queryies with WixDataQuery.or(…) .
For example:
wixData.query('Members')
.contains('birthday', value)
.or(wixData.query().contains('name', value))
.or(wixData.query().contains('address', value))
.find()
Please, let me know if you succeed or need any further assistance. And have fun Wix Coding!