You have to let the tippex dry before you write over it. 你必须让涂改液干了以后再在上面写字。
To protect yourself in future, all your office accoutrements should be discreetly marked with tippex, invisible ink or similar. 为了在将来保护好自己,你应该在办公室的所有装备上都仔仔细细地用记号笔、隐形墨水或类似的东西做上标记。