If you don't see the 'Add to Campaign' button in the lead/contact reports that you have created, it means the necessary permission is missing for the user.
Check the following article or the instructions below to resolve this issue.
https://help.salesforce.com/articleView?id=campaigns_reportwizard.htm&type=5
Add Campaign Members from Standard and Custom Reports
Adding members to a campaign is quick and easy when you add them from your lead, contact, and person account tabular, summary, and matrix reports.
REQUIRED USER PERMISSIONS
| USER PERMISSIONS NEEDED | |
|---|---|
| To add campaign members from a contact report: | Marketing User checked in your user information AND Edit on campaigns AND Read on contacts AND Read on reports |
| To add campaign members from a lead report: | Marketing User checked in your user information AND Edit on campaigns AND Read on leads AND Read on reports |
| To add campaign members from a person account report: | Marketing User checked in your user information AND Edit on campaigns AND Read on contacts AND Read on reports |
| Available in: Salesforce Classic and Lightning Experience |
| Available in: Essentials, Professional, Enterprise, Performance, Unlimited, and Developer Editions |
- From a report that returns lead, contact, or person account records, click Add to Campaign.
If the Add to Campaign button is disabled, modify your report to return fewer than 50,000 records.
- Enter the name of a campaign.
- Select a member status for the new members.
- Choose whether members already associated with the campaign keep their status. If you want, update their status with the one you selected for new members.
- In Lightning Experience, click Submit. In Salesforce Classic, click Add to Campaign.
- In Lightning Experience, you receive an email when adding members is complete. In Salesforce Classic, review the confirmation screen and then click Done.
Be aware of these considerations when adding campaign members from a report:
- To add members to campaigns from custom reports, the report’s primary object must be a lead, contact, or person account.
- To add members to campaigns from reports in Lightning Experience, the custom report type must include the Full Name field.
- If you interrupt the add campaign members' process, some members can still be added to the campaign. That’s because members are added in batches.
- If you edit a record during the adding process, it isn’t added to the campaign.
- You can add active leads to campaigns—not converted leads. If converted leads appear on your report, don’t worry, only the active leads are added to the campaign.
- The Add to Campaign button appears only in saved reports. The button doesn’t appear when you edit or preview a report.