SQL server has built in tools for re-indexing, backing up, and truncating log files. We may have a kbase article on using those tools but Microsoft also documents using them in SQL documentation online.
From the size of your log file, I would guess that you have the database configured to be backed up, but do not have any scheduled. The log file accumulated activity and gets cleaned out when a backup is performed.
Call your DBA and/or check out the information at https://solutioncenter.apexsql.com/how-to-create-a-sql-server-scheduled-backup/
The other thing you can do is check how many records you have in the TASKS table, with 5GB you probably have multiple years worth of information, and consider deleting the older, closed work orders.