Volver a las andadas
 

English?

Hola Robin! :)
Something like,
to go back to one’s old ways
to go back to one’s [bad] old ways
to go back to one's old tricks
to go back to one's old habits

Similar Spanish expressions -
"Volver por mis fueros" (more positive connotation, I believe)
"Volver por donde solía"

"To fall off the wagon" (Someone who goes back to the habit of drinking)
Used positively could be,
Be back on board!
Be back on top!
Be back in the groove!
(But I believe the Spanish is mainly used with a negative connotation...)