SQL command to update in VB6

That is a very dangerous thing to do: you leave yourself wide open to SQL Injection.
Never concatenate strings to form an SQL command: it's far, far too easy for the user to type SQL commands in the text box and damage or destroy your database. Always use parameterised queries. Google "Bobby tables" and you'll see what I mean...

And the direct cause of your problem is almost certainly the quotes round column name: they indicate a string to SQL so you are effectively telling it to set a string to another string, which isn't going to work.

BTW: Do yourself a favour, and stop using Visual Studio default names for everything - you may remember that "TextBox47" is the mobile number today, but when you have to modify it is three weeks time, will you then? Use descriptive names - "tbMobileNo" for example - and your code becomes easier to read, more self documenting, easier to maintain - and surprisingly quicker to code because Intellisense can get to to "tbMobile" in three keystrokes, where "TextBox47" takes thinking about and 9 keystrokes...