We submitted a paper, which is mostly experimental, to a Q1 journal. We did experiments with three different techniques. Considering this, we finished another paper which is totally different in subject than the first one. The second one is not an experimental work at all. However, in order to verify our numerical model, we validated it with the experimental results we obtained before and then continue to apply our model in the new paper with the numerical results. We send the second paper to a journal and they ask for more details on the experimental works. Can we add the previous experiments with paraphrase while they have not been published yet? If published, we can cite but I am not sure exactly what we should do. We cannot wait for the first paper to be published.
You should provide this question in a revised form as an explanation to the editor of the second paper. You might also want to provide a copy of the first paper, explaining where it is in the editorial process and point out the differences.
From what you say, there is no reason at all NOT to reuse your experimental data.
Depending on the discipline, inclusiveness is a virtue for a paper, meaning that you might actually be justified in republishing your data.
In many such situations you can use the delay in publication to your advantage. Note that very few papers are published exactly as first submitted, so you have some leeway.
In the second paper you can "cite" the first informally as a submitted work with formal citation to be substituted later. If the first paper is subsequently published before the second is finalized you just make the substitution.
But to make this work you probably need to have some assurance from the first journal that you will get published. So this works best if there is some delay in submitting the second after submitting the first. This might not apply in your case, I realize.
And, to satisfy the reviewers of the second paper you may need to make the first paper available to them. The editor will give advice on this.
This is just an auxiliary caution:
Nature.com's Meet this super-spotter of duplicated images in science papers describes Elisabeth Bik and the "phenomenon" of inappropriate data reuse.
What you describe does not seem at all inappropriate, but since Elisabeth Bik's work has become so famous in some fields (e.g. Biology) it's important to be very clear both to your editor & reviewers (and to your future readers) that you're not representing the same data twice as if it were two different experiments, lest someone assumes the worst and gives you a hard time or otherwise delays the publication process.
The other answers already offer some good strategies to do so, here I'm just highlighting some potential problems if you don't heed their recommendations.