To change the description of your affiliate program, go to Settings → General → Affiliate Program from your advertiser account.
There you will have a field named Description, from where you can make any changes you want for your affiliate program's description. Do not forget to press the SAVE button (bottom right corner)!
NOTE: Mentioning accepted or restricted traffic sources, in affiliate programs should not be added in the description, but the programs' own Terms and Conditions. These restrictions can relate, mainly, to:
- accepting Facebook promotion? Yes/No
- accepting promotion through Facebook Ads? Yes/No
- accepting promotion through Google AdWords? Yes/No
- accepting promotion through e-mail marketing? Yes/No