STEP ONE: no confidence vote - VONC
A vote would be held in the Commons. If majority of MPs vote in favour of Boris Johnson, he'll remain PM.
If they vote against him, he will be expected to resign.
After a government is dissolved in a VONC, there’s a two week grace period for former government or opposition MPs to unite to form a alliance that can command the majority of the House.
If no one's able to form a unified government during two-week period, an election will have to be called.