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Ask the store since they put it on your computer. We couldn't help you if we wanted to because of the lack of any specific information regarding this post. Please read Writing an effective Apple Support Communities question.

There is a chance that if an Apple service technician had to reinstall software

or a browser, that it (browser) may be set to an Apple store page on launch...

The default start page often is to Apple store or associated page in Safari.

If so, that may be a default Safari browser page that goes to an Apple home page.

You could go into browser preferences, to open Empty page; not 'default home' page.

Otherwise, the authorized Apple service technicians who handled your Mac, are

the best ones to inquire as to what they did to it, and to correct an issue therein.

Good luck & happy computing!