The hybrid-model (Avent et al 2017) in Differential Privacy is a an
augmentation of the local-model where in addition to N local-agents we are
assisted by one special agent who is in fact a curator holding the sensitive
details of n additional individuals. Here we study the problem of machine
learning in the hybrid-model where the n individuals in the curators dataset
are drawn from a different distribution than the one of the general population
(the local-agents). We give a general scheme -- Subsample-Test-Reweigh -- for
this transfer learning problem, which reduces any curator-model DP-learner to a
hybrid-model learner in this setting using iterative subsampling and reweighing
of the n examples held by the curator based on a smooth variation of the
Multiplicative-Weights algorithm (introduced by Bun et al, 2020). Our scheme
has a sample complexity which relies on the chi-squared divergence between the
two distributions. We give worst-case analysis bounds on the sample complexity
required for our private reduction. Aiming to reduce said sample complexity, we
give two specific instances our sample complexity can be drastically reduced
(one instance is analyzed mathematically, while the other - empirically) and
pose several directions for follow-up work.