Easy. Use a bench vise (pad the jaws with strips of aluminum) as a press to carefully press the pin partway in. Align the link, carefully press the pin the rest of the way in. Absent a bench vise, you can use a hammer and punch but will need to support the barrel lug. If you can clamp it down somehow it'll be easier. Brownells sells a bench block that makes the job easier as well.
Avoid the temptation to replace everything on your brand-new 1911 just to make it "better". Know what you're changing out and why. You may spend a lot of money fixing things that weren't broken to begin with. Shoot at least 500 rounds through it first, then decide what you don't like and want to improve. Regarding vintage 1911s, pre-1946 pistols are highly collectible in original, unaltered condition and should NEVER be refinished or modified as it completely ruins their monetary value.