Is Gas safety valve easy to install?

[Shivam Patel]

I have tenants at my property and turns out the ovens broken. I checked it out, and found that the glass panel was held by a piece of tape when the last owner sold it to me. I called and ordered a new oven and they were going to install the new oven, but said they couldn't because there's no gas safety valve. Then they proceeded to take the oven back and charged me for delivery (10%) and now I have to fix that before ordering a new oven. Is it easy to install this, plumbers cost a ton of money, I've already dished out too much into the property.Im from boonton, nj. Or know of how I can get this done cheap.