Assign the value of the textfield to a variable then use this variable in the SQL statement. I am assuming you are running the SQL in the macro.
EDITED 24/02/2016
I don’t know if the syntax and punctuation is different in Access to Base but in standard Basic in Base the code snippet below adds a record to the table Table1 where the Name field value is in the variable strnew so it will contain New Name…
strnew="New Name"
strSQL="INSERT INTO ""Table1"" (""Name"") VALUES ('" + strnew + "')"
If the value was (‘strnew’) then the Name field would contain strnew, the name of the variable. To get the contents of the variable requires the value to be ("’ + strnew + '").
Looking at the info at Use Variables in SQL. this might work -
DoCmd.RunSQL("Insert Into tantworten(IDGRUPPE,IDFRAGE,IDTESTUNG) Select " & Wert & " as IDTESTUNG, tfragen.IDGRUPPE, tfragen.IDFRAGE from tfragen")