Access to "Ancestry_com" is available through "Family History Centres" of the Church (and, some "Affiliate" Libraries).
Such access through a "Family History Centres" of the Church, is FREE; and, available to all Users/Patrons to a "Family History Centre".
Otherwise, a "Subscription" to "Ancestry_com" is required.
IF, you are a Member of the Church; THEN, the "Partner Access", as "X24Mom" has proffered, is the way to go.
IF, you are a NOT Member of the Church; and, have an "Ancestry_com" ("Subscription") Account; THEN, you will need to, check in your "Ancestry_com" ("Subscription") Account to see how you link 'Family Tree" of 'FamilySearch' to "Ancestry_com"; OR, contact 'Customer Service' of "Ancestry_com" for help.
From a "Knowledge Article" in 'FamilySearch':
• Online: https://support.ancestry.com/s/
• Email: [email protected]
• Phone: The number varies depending on what country you are in. For a list of phone numbers, visit https://support.ancestry.com/s/phonesupport
Note: Some countries have a separate Ancestry website, and the contact information is only found on that site. For example, Mexico's Ancestry website is ancestry.mx.
I hope this helps.