Hello, Cristina,
Thank you for contacting us and for using XStore.
To add a search widget to the Shop sidebar, please navigate to Appearance > Widgets. If this is not what you are looking for, please provide us with more information and screenshots.
You can use screenshot tools such as Lightshot or Gyazo and share the links here. Alternatively, you can use a file-sharing service such as WeTransfer https://wetransfer.com/.
We appreciate your cooperation and look forward to hearing from you soon.
Kind Regards,
8theme team