Hi @Anonymous ,
Is StudentName is singleLine and Subject in List one is Choice type?
I test as next with two methods:
- List one columns: StudentName(SingleLine), Subject(Choices), Grade(Number)
- Method1:
- List two columns: StudentName(SingleLine), Subject1(SingleLine), Grade1(Number), Subject2(SingleLine), Grade2(Number), Subject3(SingleLine), Grade3(Number)
- Method2:
- List two columns: StudentName(SingleLine),S_M(SingleLine),GM(SingleLine)
App test:
Method1:
Add one dropdown control and rename it Dropdown1_Sname,Dropdown1_Sname.Items:'20190401listone'.StudentName
Add three combobox controls, and rename them as ComboBox1_Subject,ComboBox1_Subject_2ComboBox1_Subject_3, their Items are same:ComboBox1_Subject/ComboBox1_Subject_2/ComboBox1_Subject_3.Items:Choices('20190401listone'.Subject)
Add three textinput controls,and rename them:TextInput1_Grade,TextInput1_Grade_1,TextInput1_Grade_2.
Then add one button, and rename it Button_Method1,Button_Method1.OnSelect:UpdateIf('20190401list2',StudentName=Dropdown1_Sname.Selected.StudentName,{Subject1:ComboBox1_Subject.Selected.Value,Subject2:ComboBox1_Subject_2.Selected.Value,Subject3:ComboBox1_Subject_3.Selected.Value,Grade1:Value(TextInput1_Grade.Text),Grade2:Value(TextInput1_Grade_1.Text),Grade3:Value(TextInput1_Grade_2.Text)})

Method2:
Add one dropdown control and rename it Dropdown1_Sname,Dropdown1_Sname.Items:'20190401listone'.StudentName
Add one combobox control, and rename it ComboBox1_SubjectM2,ComboBox1_SubjectM2.Items:Choices('20190401listone'.Subject)
Add one textinput control and rename it as TextInput1_GradeM2
Add one Button control and rename it Button_Method2,Button_Method2.OnSelect:UpdateIf('20190401list2',StudentName=Dropdown1_Sname.Selected.StudentName,{S_M:Concat(ComboBox1_SubjectM2.SelectedItems,Value&","),GM:TextInput1_GradeM2.Text})

Check the SP list:

Hope this could be helpful.
Best Regards.
Yumia