How would you try to get your girlfriend to tie you up?

Start a conversation about what her fantasies are. She will ask about yours most likely and you can tell her. Be prepared (personal boundaries accepted) to act out her fantasies with her, she should then be more open to indulge yours.

Of course
It’s the best way forward

It would be a waste of time. She can't tie a good knot, and every rope would be tied in a neat bow.

A few questions... Have you had sex with this person before?

Do you live together?

Do you plan on being with them long term?