Consider this option:
Students who would have gone to the lab today will instead go there tomorrow.
Part of the problem with your original sentence is that the "would" of "would go" could be either the past-tense form or the subjunctive form of the auxiliary "will". In the past tense, "would go" can mean something like "had the habit of going". In the subjunctive mode, it can mean something like "have the (conditional/hypothetical/potential/etc.) intention of going".
If I understand your context correctly, you want to use both the subjunctive mode (to indicate that going today is contrary to fact, that it didn't happen and won't happen) and the past tense (to indicate that the intention, even if merely hypothetical, no longer exists in the present).
For this verb, like most verbs, the past-tense and subjunctive forms are identical. There is no sensible way in English to combine the two. However, we can easily combine the subjunctive mode with the so-called perfect aspect. In turn, the perfect aspect implies an occurrence in the past because it expresses some result of that occurrence.
The verb phrase "would have gone" displays the active voice, subjunctive mode, present tense and perfect aspect.
Another part of the problem is that going today didn't happen, so "going again" doesn't make sense. Visiting the lab tomorrow is a replacement for visiting the lab today, not an addition to it.
There are ways to use the word "again" which do make sense. For example:
Students who would have gone to the lab today will try again tomorrow.
This sentence implies that the students made an attempt today, although the attempt was unsuccessful. Trying to visit the lab tomorrow is an addition to having already tried today.