Measure / Observe of noise on DC voltage using oscilloscope

[xchg.ca]

I have Hantek dso5102p and want to check noise part of DC voltage.
But I have problem -  to see noise part I have to switch to mV ranges in same time DC voltage has to be in V range, and vertical position cannot really help ( still off screen )
It seems like the scope does not have ability to specify DC offset to compensate, for example -12V ? Unless I do not know what I'm looking for. May be people familiar with Hantek dso5102p can help me.
Also the same problem on analog Tektronix 2252
May be there is a technique of some kind I can employ?

Thank you

[bdunham7]

In your channel menu do you have an option for AC coupling?  Typically the options are DC, GND and AC.  AC will switch in a blocking capacitor to keep out the DC.  Do not do this with high voltage DC greater than the rated input of the scope (not the probes).  Your Tek 2252 definitely has this feature, the buttons are right above the CH1 and CH2 inputs.