Google Nexus 5 — Difficulty in reinstating text icon

Dear All,
Have just bought a S/H Nexus 5 and in trying to remove as many battery draining icons, I have "lost" the Text icon.
This was fine by me, as I have only ever texted twice in my life. However today my phone provider decided to text an activation key to me, instead of enclosing it in an email.
I've forgotten how I deleted it and have tried a number of ways to reinstate it, to no avail.
Can anyone help please?
John