Odawara is easy to access from major cities and airports in Japan. From Tokyo, Osaka, Kyoto or Nagoya, take the bullet train, Tokaido (Tokaido -Sanyo) Shinkansen train, to Odawara Station.
https://global.jr-central.co.jp/en/

The ways from the airports (Narita and Haneda) to Odawara Station.
First, when you arrive at an airport and exchange money for Japanese yen, get at least several 1000 yen bills because a 5000 yen bill or 10000 yen bill is often not accepted by machines.
If you stay in Japan for a while after the Conference, you may better rent a mobile WiFi at the airport, although a reservation may be necessary.

If you arrive at Narita airport:
From Narita Airport Station, move to Shinagawa Station by train (by Narita Express).
https://www.jreast.co.jp/multi/en/nex/

At Shinagawa Station, change trains. Then, you can move directly to Odawara Station by train (Tokaido Shinkansen Line). There are several types of trains on the Tokaido Shinkansen Line, and among them all Kodama type and some Hikari type trains stop at Odawara Station (Note: Other types of trains do not stop at Odawara Station).
Note: You can change trains also at Tokyo Station but Shinagawa Station is more convenient for transfer.

If you arrive at Haneda airport:
From Haneda please go to Shinagawa Station by train (Keihinkyuko Line = Keikyu Line). At Shinagawa Station, change trains. Then, you can move directly to Odawara Station by train (Tokaido Shinkansen Line). See above.

Try this website for train transfer information.
https://world.jorudan.co.jp/mln/en/

From Odawara Station, the free shuttle bus is available to the hotel, but the service from Odawara Station is only through Mon-Fri and only during day time. Free shuttle bus is available from the hotel-nearby Nebukawa Station (2-3 services/hour, daily).
See the hotel web page below for the regular shuttle bus schedules.
https://odawara.hiltonjapan.co.jp/pdf/access/shuttle_bus_schedule.pdf

Extra Bus Service

In addition to the regular shuttle bus service, extra bus service is provided for the participants. The bus departure point at the Odawara Station for extra buses is the same as for regular shuttle buses and is outside the Odawara Station. Below is the schedule.
・Oct. 17(Mon) 21:15 Hilton → Odawara St.
・Oct. 18(Tue) 07:20 Odawara St. → Hilton
21:15 Hilton → Odawara St.
・Oct. 19(Wed) 07:30 Odawara St. → Hilton
21:15 Hilton → Odawara St.
・Oct. 20(Thu) 07:30 Odawara St. → Hilton
21:25 Hilton → Odawara St.
・Oct. 21(Fri) 07:10 Odawara St. → Hilton
13:20 Hilton → Odawara St.
13:30 Hilton → Odawara St → Tokyo St.

The map of the bus departure point outside the Odawara Station West Exit is found on the following Japanese web page.
https://www.hiltonwedding.jp/odawara/access/
A shuttle bus from Nebukawa Station departs from just outside the exit (there is only one exit). Please note that Nebukawa Station is a small rural unmanned train stop and there is no elevator or escalator. Stepping the stairs is necessary inside Nebukawa Station.
It is also possible to take a taxi from Odawara Station, and sharing a taxi with other participants is recommended to save taxi fares. There are many taxis in Odawara Station but not in Nebukawa Station.