Potential of a body is defined as the amount of work done in bringing that body from infinity up to some point divided by its charge.
The Earth has zero net charge, so the work done in bringing any charge from infinity till the Earth is zero.
So what do statements like, "The potential of this body wrt Earth is +5V" or "This positively charged body has positive potential and on grounding, the charge flows into the ground to make it's potential zero" mean ?