  HESS J1702-420 is a peculiar TeV complex with a morphology changing from a
diffuse (HESS J1702-420B source) at $\lesssim 2$ TeV to point-like (HESS
J1702-420A) at $\gtrsim 10$ TeV energies. The morphology and the spectral
properties of HESS J1702-420 could be understood in terms of a (diffusive)
hadronic or leptonic models in which the observed TeV emission arises
correpondingly from proton-proton or IC-radiation of relativistic particles
present in the region. In this work we perform searches of the X-ray
counterpart of HESS J1702-420B source originated from the synchrotron emission
of the primary or secondary relativistic electrons produced within leptonic or
hadronic models. Such an emission can be extended and remain beyond the
detection capabilities of a narrow-FoV instruments such as XMM-Newton. We
utilise the publicly available first 6-months eROSITA dataset (DR1) fully
covering selected for the analysis region of $> 5^\circ$-radius around HESS
J1702-420. We discuss biases connected to variable plasma temperature/neutral
hydrogen column density in the region and present results based on background
modelling approach. The performed analysis does not allow us to detect the
extended X-ray counterpart of HESS J1702-420 of $0.07^\circ - 3^\circ$-radii
sizes. The derived upper limits are significantly higher than the expected
hadronic model flux of the X-ray counterpart. For the leptonic model the
derived limits indicate the magnetic field in the region $B\lesssim 2\mu$G. We
argue, that the further advances in the diffuse X-ray counterpart searches
could be achieved either with next generation missions or Msec-long
observational campaigns with currently operating instruments.
