In Wise.blue, open the 3 dots contextual menu next to the account name and click Edit.
Under Advanced find Custom Audiences and click the + Upload Audience button.
Name the audience, select the suitable type of the audience in Audience type and choose the X account to which you wish to upload the audience list.
Press Next and upload the audience.
The list will take 72 hours to be approved by X. Until then the audience status will show as "too small".