Add textbox value to it's destination - vba

Question

Situation: I'm working on a UserForm with the following Controls:
Combobox: This is used to pull up a list of names on Sheet2 (Column A) and allows the user to select a name that'll be used for the form.
TextBox: This is used to add a numerical value. That value will be placed on Sheet2, Column C, and two rows over from the name that's been selected from the combo box
CommandButton: This button is used to add the numerical value that has been typed into the text box into the cell on Sheet2, two columns over, and two rows over from the cell matching the name that's been choosen from the combobox
Problem: I have the Combobox and Textbox set up correctly but am having trouble creating VBA for the CommandButton to add the text box value to it's destination.
VBA So Far:
Private Sub AddButton_Click()
Dim WS As Worksheet
Dim Rng As Range
Dim Crystal As Long
Set WS = Worksheets("ParticipantList")
With WS.Range("a2:c300")
FindColumn = Application.WorksheetFunction.Match(Me.Participants.Value, WS.Range("A2:A300"), 1)
Crystal = Me.NumberOfCryst.Value
If FindColumn <> "" Then
With WS.Range("a2:c300")
Text = Me.NumberOfCryst.Value
WS.Activate
FindColumn = Application.WorksheetFunction.Match(Me.Participants.Value, WS.Range("A2:A300"), 0)
End With
End If
End With
End Sub
Now obviously this is all over the place and I've made tons of changes and attempts at getting it to work.

Answer 1

maybe you're after something like this:
Private Sub AddButton_Click()
Dim Rng As Range
Set Rng = Worksheets("ParticipantList").Range("A2:A300").Find(What:=Me.Participants.Value, LookIn:=xlValues, lookat:=xlWhole)
If Not Rng Is Nothing Then Rng.Offset(2, 2).Value = Rng.Offset(2, 2).Value + CLng(Me.NumberOfCryst.Text)
End Sub
you may also want to add some textbox text validation and be sure the user input a numeric value