It is tough to estimate how much and how long your credit score will get affected as a lot of factors go into computing the credit score. However, a credit card settlement will influence your credit score negatively and will remain in your credit report for up to 8 years unless you clear your outstanding dues.
If you are already having another loan or credit card and you are regularly repaying it for about 2 years, there are chances to keep your score intact. However, when the lenders check your credit report, your settlement might lower your chances of getting future credit. Hence it is recommended to clear your past dues and get back on track to good credit health.