Don't let anyone give you shit for asking. No one is born knowing how to reconstitute peptides, so we all learned sometime.
In terms of how to do it materially, you add bacteriostatic water to the peptide vial via syringe. Swab the tops with alcohol first, then take bac water out of a vial of bac water with a syringe, and transfer it into the peptide vial. Because both of those are sealed to air, you may want to suck some of the air out of the peptide vial first. That way, as you add the water, you don't have to press so hard to get more in because the air pressure inside won't keep pressing back. (I know you don't need this much detail but someone in the future will.)
The part I think you're asking is figuring out quantities. The governing equation is:
[Eq1] m1 / v1 = m2 / v2
where
m1 = mass of peptide that came in the vial (mg or IU)
v2 = the volume of bac water you added to the vial (mL)
m2 = the mass you want to inject with each dose (mg or IU)
v2 = the volume you need to inject to get that mass (mL)
If you want to know where that equation comes from, it's the idea that the concentrations of what you mix is the concentration of what you inject. Since concentration is mass/volume, you know that the two are equal (c1 = c2) and that's it.
The smart way to figure how much to reconstitute with (imo) is to first consider the volume you want to inject. You don't want the peptide to be so dilute that you have to inject 5 mL every time. You also don't want it to be so concentrated that you only inject 0.05 mL -- you'll spill a full dose every time, and most syringes aren't good at measuring really small quantities. If I have 1 mL syringes, I like the doses to be between 0.2 and 0.5 mL. If I have a 0.5 mL syringe, I want it to be between 0.1 and 0.4 mL. Those are both small amounts to inject and easy volumes to measure accurately.
For MT2, I think the dosing range is usually 0.25 to 1.0 mg. Let's pick 0.5 mg because it's in the middle. And, since you might want to use more as you acclimate, let's just make that a rather small injection, just using 0.2 mL as our injection volume. To determine the volume you want to add, you first rearrange Eq1 above to solve for v1:
[Eq2] v1 = m1 v2 / m2
Then just plug in values:
v1 = (10 mg * 0.2 mL) / 0.5 mg
v1 = 2 mL / 0.5 = 4 mL
So, if you add 4 mL to the vial to start, every 0.2 mL gives you a dose of 0.5 mg.
Even if the number comes out to something really unclean for the volume you put in the vial in the beginning (v1), it isn't that big of a deal because you only have to measure it once. So if the answer came out to 3.07 mL, you add 3 mL and do you best to try to add that 0.07 mL. That is a pain in the ass, but it's a pain in the ass once. This is really handy when people have a Jano test that says your 5 mg vial actually contains 4.72 mg... you plug 4.72 into the calculator, use the same target dose/volume, and it tells you how much to add that first time.
I know you said you have a calculator, but I made one for a friend who was using semaglutide. You can input your values in the blue boxes, and it spits out the volumes and masses in the green ones. That way, if you alter your dose of MT2 and want to inject 0.66 mg one day after you've already reconstituted, you just plug that in and it tells you the volume to pin.
Here's a link.
