How to set a checkbox status as True / False within a IF-THEN statement using vb.net

I am trying to automate a scenario using silk test and am very new to coding using vb.net. Basically i have a checkbox identified and want to set it to either true or false based on a string value being passed.

for e.g.

Dim tfnSigned As String
tfnSigned = "Yes"
If tfnSigned = "Yes"
Then .CheckBox("SED_TFNSignedCheckBox").Check
End If

In this case, i get a compiler error as .CheckBox is not identified as a class and hence cannot use the Check method

Kindly help

Cheers