Typically, such GSEC and SDL bonds
will NOT have any liquidity in the secondary markets (NSE, BSE).
One usually holds them till maturity
and receives the entire face-value of the bond upon maturity,
earning interest on it for the duration one holds the bond.
Interest (every 6 months) and principal (upon maturity) are received automatically in the bank account linked to the demat account holding the security.
To get rid of such illiquid bonds in a hurry on the secondary markets (NSE/BSE)
the strategy is to basically offer all the bonds one is holding
and sell-off whatever quantity (even part of one’s entire holdings) one can
at progressively lower rates (even lower circuit limits),
as circuit-limits reduce further each day after a trade occurs at a lower price.
For more details, checkout this topic-thread where this scenario was recently discussed.