Someone added custom CSS rules to your site.
Look in the theme Custom CSS or under Store Locator Plus > Settings > View additional CSS.
This rule is pushing the button to the far left:
flex-direction: row-reverse;
Removing that will put the button on the left. You can set right padding to adjust as necessary.
Whomever is editing your CSS seems to have a clear understanding of CSS rules and should be able to handle this for you.