Normally this is not a problem in design. Usually when you for example use standard small VIA like 0.45mm diameter / 0.2 hole, then even if you place the VIAs the way they would be touching, the distance between holes will be 0.45mm.
So the problem is mostly about VIAs in same net (e.g. VIA array in Exposed pad) or if you are creating non plated holes (they do not have ring around them, so it may be easy to place them close to each other).
If you need you can set specific rule in Design Rules -> Manufacturing -> Hole to Hole clearance
For the VIAs in pad, I think you may use Design Rules -> High Speed -> Vias under SMD (I am not 100% sure, you can try, let me know
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