Create an option to personalize the product you buy (Tennis Rackets) - Shopify

In each product of the specific collection of Tennis Rackets of www.volealo.com, I want to give the consumer the option to string (or not) the racket, which means he has to chosse the kind of string he wants + tension of the string.
Some examples from competitors are the following:
https://www.mistertennis.com/es/babolat-pure-drive-raqueta-de-tenis-101552.html
https://www.tenniswarehouse-europe.com/Raqueta_Babolat_Pure_Drive_2025/descpageRCQBA-BPD25R-ES.html
https://www.tradeinn.com/smashinn/es/babolat-raqueta-de-tenis-junior-pure-drive-26/140436599/p