So, what "immediate" steps does Trump want to be taken? Consistent with the Constitution, I mean.
The problem is that the Constitution expects honest elections to be held by each state, thus the Constitution has no method for addressing the problem. Thus far, the parties that "should" be addressing the problem (state legislatures) have refused to do so.
Congress could, of course, impeach Biden and Harris, but given the RINO population in the Congress, that remedy is unlikely.