You can modify the EL by following the steps outlined in this article: https://proconnect.intuit.com/community/tax-organizer/help/using-intuit-link-in-lacerte/00/5170

When your client logs into Intuit Link, there will be a section called Engagement Letter, which says Pending.  After clicking on that section, your client will see the entire content of the EL.  At the bottom of that screen, there is a box into which your client should type in his/her name.  He/she would then click on the Accept button to electronically sign the EL.

Once that's signed, you will see the status updated in Intuit Link and can proceed download the signed EL.  Don't expect anything fancy though.  All that it'll show is the name as typed in by your client and the date on which it was accepted (aka signed).  You won't get any metadata related to that "electronic signature" or the signed document.  In other words, you may want to consult your attorney if you worry about whether it is legally acceptable.

Since you are new to Intuit Link, you should invest some time testing out Intuit Link, both as the accountant and a client, to understand its workflow, setup, limitations, and how it fits into your business process, which may need to be realigned or modified if you decide to use Intuit Link as your client portal. 

This is important because you will likely receive calls and emails from your clients about the use of Link, especially when they run into problems, to help them diagnose those issues and suggest resolutions.  Every year, we see a number of questions from both accountants and users alike about problems they encounter while using Intuit Link.

If your clients are not very tech savvy, Intuit Link may not be the best option for them but only you will be able to make that determination and you won't be able to make that determination until you have familiarized yourself with how it works, in both the accountant and client portals.

Hope this helps.