This script helps you with removal of all artifacts in a project.

gitlab-remove-all-artifacts.sh

#!/bin/sh

#<your project id (you can find it with inspect element on the project page)>
PROJECT_ID=36944
#<your access token (can be generated in your profile settings)>
ACCESS_TOKEN=xxxxx-XXXXXXXXXXXXXXXXXXXX
#<your gitlab instance hostname (ex. gitlab.lrz.de)>
GL_SERVER=gitlab.lrz.de

for PAGE in $(seq 1 1000); do
    echo "Currently on page ${PAGE}"
    JOBS=$(curl --globoff --header "PRIVATE-TOKEN: ${ACCESS_TOKEN}" "https://${GL_SERVER}/api/v4/projects/${PROJECT_ID}/jobs?per_page=10&page=${PAGE}")
    JSON_EXT=$(echo $JOBS | jq 'map(.id)')
    echo $JSON_EXT

    echo $JSON_EXT | jq -c '.[]' | while read job_id; do
        curl --request POST --header "PRIVATE-TOKEN:${ACCESS_TOKEN}" "https://${GL_SERVER}/api/v4/projects/${PROJECT_ID}/jobs/${job_id}/erase"
    done
done