Is there a way that you can make a wait step that waits until the first of the following month?
Trigger happens on April 14th that updates a data value then waits until May 1st to then update another field.
You can change the wait step to a date, instructions here: Use a Specific Date in a Wait Flow Action - Marketo Docs - Product Docs
I was hoping to come up with a wait step that would also work for the following month if the next trigger happened of September 6th --> October 1st.
So rather than doing this as a wait step, you could consider adding them to a static list, then have a recurring batch campaign run on the first of each month to do the action you wanted. Once this action is completed, you can run them through the additional set of flow steps.
This is also possible using an engagement engine campaign. Otherwise, there is no wait step available that waits till first of the month