"Write via computer" can be expressed as "compose using a computer" or simply "type on a computer".
The phrase comes from the widespread usage of computers as a tool for composing and typing text, whether for personal or professional purposes.
Example sentences:
"I usually write my emails via computer, it's faster and more convenient."
"She spends hours typing on her computer, writing her next novel."
Example translations:
"我通常通过电脑写电子邮件，这样更快更方便。"
"她花数小时在电脑上打字，写下她的下一本小说。"