You mean to figure out what month +1Month would move to?

Yes, that's exactly what I mean. Because if I know what the next month is, I can also take the previous month. Attaches picture

Something like this would give you last months name, the current month, and next months name. Just change the Date() field to the date field that sets your current month.

    MsgBox MonthName(Month(DateAdd("m", -1, Date)))
    MsgBox MonthName(Month(Date))
    MsgBox MonthName(Month(DateAdd("m", 1, Date)))

Can I use a Dropdown Box to select Current Month from and return the Previous Month and Next Month values ​​in the text boxes?

(Don't know where this came from​​)
Can I use a Dropdown Box to select Current Month from and return the PreviousMonth and NextMonth values in textboxes

Sure, you should already have a date field somewhere though that sets up your calendar. That would probably be the easiest.

But if you want a combo box to select a month, you might need a little more vba to create a date field out of a combo box. The easiest way would probably be to store the month number inside the combo box along with the month name, so you wouldn't need to figure that out.

Do you think that is too difficult for me to understand?
Sounds like a good idea to store the month number inside the combo box along with the month name.
But it sounds exciting with VBA programming.

No but I mean if you already have the date field, you could just automatically populate the previous and next months names onto the buttons and just put it into your current coding for +1Month etc. It's a lot simpler and streamlined.

If you want to do a combo box though, make it 2 columns, with a row source like this.. Bound column 1
1;"January";2;"February";3;"March";4;"April";5;"May";6;"June";7;"July";8;"August";9;"September";10;"October";11;"November";12;"December"
You can set the width of the first column to 0 so you only see month names.

Then you can just do textboxes with control sources like
=IIf([MyCombo]=12,"January",MonthName([MyCombo]+1)) 'for next month
=IIf([MyCombo]=1,"December",MonthName([MyCombo]-1)) 'for prev month

I usually use a For Next Loop to add months to a Combo Box.

    Dim X As Long, S As String

    For X = 1 To 12
        S = X & ";" & MonthName(X)
        cboMonth.AddItem (S)
    Next

Glossary: MonthName