How to file return with LLC business operations suspended?

My wife and I have had a single-member LLC for several years with revenue, expenses, home office, depreciation, etc. For personal reasons, for tax year 2018 (filing under an extension) and 2019 we have had no revenue-producing activity. We fully expect to resume all activity in 2020. How do we file 2018 and 2019 so as to maintain continuity?