You can put in an estimate of your spouse’s net income (line 23600) for now, and then before you file, you can go back and put in the correct income amount. You can put in the estimate based off of their income from the previous tax year.

FYI: As the spouse of someone with Self-Employment income, your tax return is also not due until June 15, 2021. However, both you and your spouse still have to pay any balance owing by April 30, 2021. The CRA has a full list of tax return deadlines here: https://www.canada.ca/en/revenue-agency/campaigns/covid-19-update/covid-19-filing-payment-dates.html