Fully agreeing on the comment of h.mon. RNA-seq data are not normally distributed. Plot a histogram of the counts and you will see it without any test. DESeq2 models counts as a negative binomial. There is no need to filter anything, check for any distribution (if you have standard RNA-seq data) or apply any outlier (or something else) correction. Please start with your raw HTseq counts and follow the DESeq2 manual. If there was the need for any actions to be taken it would be in the DESeq2 manual.
Please, provide more details and put some more effort in your question - for example, provide some background on why you want to perform these tests, what have you read so far, and so on.
It is widely known and accepted RNAseq count data does not follow a normal distribution, rather, it is better modeled as a negative binomial distribution. See some old posts: