As the Guardian reported
Farage began the party’s election campaign last week saying he would put up candidates across the country unless Johnson abandoned his Brexit deal and formed a leave alliance. [...]
Farage offered Johnson a deal last week in which his party would stand down in seats where the Tory candidate believed in a no-deal or “clean Brexit” and would want to abandon Johnson’s deal. In return, he wanted his party to have a free run at Labour heartland seats.
I suppose there is a deadline for entering candidacies, but is there one for withdrawing from the election thereafter? Can candidates formally drop out of the race any time thereafter?