Reduce the spectrum noise of plomb function

i have pressure data with non-uniform spaced time sample as show below x-axis is the time in second and y-axis is the pressure values

as the i have non-uniform spaced time samples, i used plomb funnction to get power density spectra

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[pxx1,f1]=plomb(p0-mean(p0),t,20000);

pxx1=10*log10(pxx1/10^5);

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I got this resutls

is there any way to use DFT averaging using windowed segments as in Pwelch function to reduces the variance σ2 of the noise spectrum ?