Use CONNECT or SIGNET in the CONFIG menu to edit these settings automatically:

[BLOCKCHAIN]
# options: bitcoin-rpc, regtest
blockchain_source = bitcoin-rpc
network = mainnet
rpc_host = LAN_IP_ADDRESS or .onion
rpc_port = 8332
rpc_user = RPC_USERNAME_OF_THE_CONNECTED_NODE (as in the bitcoin.conf)
rpc_password = RPC_PASSWORD_OF_THE_CONNECTED_NODE (as in the bitcoin.conf)
rpc_wallet = fill a wallet name from Bitcoin Core ('bitcoin-cli listwallets')

The Yield Generator is configured in the joinmarket.cfg since JoinMarket v0.8.1.
Use the RESET option in the CONFIG menu to return to the defaults options:

[YIELDGENERATOR]
# [string, 'reloffer' or 'absoffer'], which fee type to actually use
ordertype = reloffer
# [satoshis, any integer] / absolute offer fee you wish to receive for coinjoins (cj)
cjfee_a = 500
# [fraction, any str between 0-1] / relative offer fee you wish to receive based on a cj's amount
cjfee_r = 0.00002
# [fraction, 0-1] / variance around the average fee. Ex: 200 fee, 0.2 var = fee is btw 160-240
cjfee_factor = 0.1
# [satoshis, any integer] / the average transaction fee you're adding to coinjoin transactions
# (note: this will soon be deprecated; leave at zero)
txfee_contribution = 0
# [fraction, 0-1] / variance around the average fee. Ex: 1000 fee, 0.2 var = fee is btw 800-1200
txfee_contribution_factor = 0.3
# [satoshis, any integer] / minimum size of your cj offer. Lower cj amounts will be disregarded
minsize = 100000
# [fraction, 0-1] / variance around all offer sizes. Ex: 500k minsize, 0.1 var = 450k-550k
size_factor = 0.1
gaplimit = 6

Find all the defaults at:
https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/master/jmclient/jmclient/configure.py#L101