2014 Maxforce N13 in Prostar w/ sleeper RED Octagon light w/ engine light

Live in MN have not run for couple months. Have 660K on engine.
Didn't want to start after sitting few weeks so have started and let idle a couple hours a few times over last 3 weeks. A week ago when I shut it off after idling the check engine light was on.
Went to go for a load yesterday started it and the engine light was on and minute after I started it the Red Octagon came on. ( OK now were going to get serious right) I shut it off checked the dash where codes may display and it said low coolant. ( yes I know should have seen in Pre Inspection.) I filled the coolant with about 3/4 gallon and started truck again for few minutes and Red Octagon Light did not come on but Check engine light still on. shut off again cause by this time missed load pickup and trying to figure out what to do. Afraid to drive down road and see if other light goes out or Red one comes back on. Wondering if I should invest in a Tool to read codes and one that can do a forced regen. or just take to a shop and hope don't get side of road on way. Any one have/ know tool that will do forced regen on 2014 Max N13??
Any suggestions on any of this???
PS: I have had truck for about a year and have put 60 K on it without any issues with DPF system. Have never done a parked regen and have had check engine light come on before but went out after driveing again so figure it was DPF and worked itself out after running a bit.